code: def start_prometheus_http_server():
      if start_http_server:
          start_http_server(_PROMETHEUS_CLIENT_PORT)
  
file_path: mars/mars/metrics/backends/prometheus/tests/test_prometheus_metric.py
imports: import pytest
  import time
  from .....utils import get_next_port
  from ..prometheus_metric import Counter, Gauge, Histogram, Meter
label_desc: Use image node_id 1 for calling a global function with example usage: start_prometheus_http_server() without return types